1. Field of the Invention
This invention relates to the control of the electrical loads, and, more particularly, to the control of two different electrical loads and selected auxiliary loads through sequential operation of a remotely placed single pole, single throw (SPST) switch.
2. Description of the Prior Art
Two United States Letters Patent have previously issued to the inventor hereof for control of two speed motors. The first is U.S. Pat. No. 3,097,331, dated July 9, 1963, and the second is U.S. Pat. No. 3,327,192, dated June 20, 1967.
The '331 patent describes a two speed split phase motor controlled by a remote SPST line switch through a single pole, double throw (SPDT) relay disposed externally of the motor. The '192 patent describes a two speed split phase motor, again controlled by a remote SPST line switch. In the '192 patent, the motor controlling relay is combined in the motor starting switch and is disposed in the switch end bell housing of the motor. The internal motor switching of the '331 and '192 patents, and of the motor discussed herein, includes the centrifugal switch system normally found in fractional horsepower split phase motors. That is, utilization is made of the rotational speed of the squirrel cage rotor in switching from the motor starting circuit to a sustained speed motor run circuit.
Included in both prior art patents are mechanical movements of the centrifugal switch associated with the switching from motor starting to a sustained motor running speed.
Also included in both prior art patents are relay and line switch contacts which carry the full current drawn by the operational motor during a period of contact bounce and seating on first closure of the contacts. The use of mechanisms and switch contacts impose certain limitations on reliability and longevity of the system in these types of apparatus. Inevitably, mechanical movements result in contact arcing and wear and other problems associated with repetitive mechanical switching. Hence, the employment of relay contacts carrying heavy currents results ultimately in the deterioration of mechanical functioning, and in the burning, pitting, and sticking of contacts. These factors tend to cause the entire apparatus to fail. For apparatus with solid state electronic switching, in which there are no moving parts, the inherent problems associated with mechanical movements and relay contacts are substantially eliminated.
Prior to the advent of the apparatus of the '331 patent, now commonly used in ducted evaporative cooler installations, the prior art consisted of running a third wire from a SPST line switch through a SPDT switch to a two speed motor. In a three wire branch circuit, one wire was serially connected to the common terminal, a second wire to the low speed terminal of the motor, and a third wire to the high speed terminal of the motor. In original installations the cost of running a third wire in the appliance branch circuit serving the two speed motor is quite modest. However, when a previously installed single speed motor is to be replaced by a two speed motor, installation of a third wire in the permanent appliance branch circuit is both time consuming and relatively expensive.
"Pulling" a third wire carries the additional requirements of (1) an electrical permit, (2) preliminary installation and inspection, (3) final installation and inspection, and additional switches, receptacles, appliance cords, and the like. Thus, both considerable time and expense are involved in the replacement of an installed single speed motor with a two speed motor. It is obvious that the apparatus of the present invention, and the apparatus of the '331 and '192 patents, offers an inexpensive and quickly installed alternative to providing a third wire in the appliance branch circuit.
In the present apparatus, the provision for single speed motor control by means of a single pole single throw line switch is extended for operational control of a two speed motor. This provides a simple, relatively inexpensive, and highly desirable alternative to installing a third wire in the appliance branch circuit in order to operate a remotely placed two speed motor.
The apparatus of the present invention includes features not found in either the '331 or the '192 patents. These features include a "soft start" of the motor in which the inrush current to the motor windings rises slowly during the starting procedure. Also included is start capability by means of an additional, remotely placed, signal circuit operating switch. A flip-flop turn-on circuit is used to give sequential operational control responsive to randomly timed signal circuit impulses. Fault/overload protective circuits are used to shut down the operating system on occurrence of a system fault or overload in the load operating circuits.
The apparatus of the present invention overcomes the undesirable aspects of the third-wire prior art, and diminishes or eliminates the threats to reliability and longetivy which may occur in the apparatus of the '331 and '192 patents.